Because of the recent technological advancement in such areas as micro fabrication, liquid crystal material, packaging and the like, liquid crystal panels with a display screen measuring diagonally from 5 cm to 50 cm, which allow television pictures and various video images to be displayed flawlessly in practical use, are made available on a commercial basis.
Also, a liquid crystal panel, which displays images in color, is realized without difficulty by having one of the glass substrates, which constitute the liquid crystal panel provided with a RGB colored layer.
Particularly, with a liquid crystal panel having a switching element built in each respective pixel, the so -called active type liquid crystal panel, the displayed video images have little cross-talk, a quick response and a high contrast ratio.
Each of these liquid crystal panels has usually a matrix composition of 100 to 1000 scanning lines and 200 to 2000 signal lines, respectively, and an effort in development on both a larger screen size and a higher resolution has recently been under way to cope with the requirement for enhanced display capacity.
FIG. 4 is a perspective view of part of an active type liquid crystal panel and an active type liquid crystal panel 1 is formed of an active substrate 2 and an opposing substrate 9 with liquid crystal filled therebetween.
The active substrate 2 comprises:
a translucent insulating substrate; PA1 a plurality of scanning lines disposed on one of the main surfaces of the translucent insulating substrate; PA1 a plurality of signal lines intersecting generally at a right angle with the scanning lines; PA1 at least one or more of insulating layer sandwiched between the scanning lines and the signal lines; PA1 at least a switching element and a pixel disposed at each respective point of intersection of the scanning line and signal line; and PA1 a cluster of terminal electrodes of the scanning lines and signal lines disposed outside the image display area of the active substrate 2. PA1 a first translucent insulating substrate; PA1 a plurality of scanning lines disposed on one of the main surfaces of the first translucent insulating substrate; PA1 a plurality of signal lines intersecting generally at a right angle with the scanning lines, respectively; PA1 at least one or more of insulating layer sandwiched between the scanning lines and the signal lines; PA1 at least a switching element and a pixel at each respective point of intersection of the scanning line and signal line; and PA1 terminal electrodes of the scanning lines and signal lines disposed outside the image display area of the active substrate, and PA1 a second translucent insulating substrate with a translucent conductive layer disposed on one of the main surfaces thereof; or PA1 the second translucent insulating substrate with a color filter layer formed thereon, and PA1 having an opening, which is formed over the opaque film and the conductive patterns, filled with a translucent resin and applied with a pressing force to establish connections between the conductive patterns of the TCP film and the terminal electrodes; and PA1 having light rays irradiated from the side opposite to the surface of the TCP film provided with the conductive patterns on the joint surfaces between the conductive patterns and the connecting terminals through the translucent resin to harden the photo-curing resin. PA1 a first translucent insulating substrate; PA1 a plurality of scanning lines disposed on one of the main surfaces of the first translucent insulating substrate; PA1 a plurality of signal lines intersecting generally at a right angle with the scanning lines, respectively; PA1 at least one or more of insulating layer sandwiched between the scanning lines and the signal lines; PA1 at least a switching element and a pixel at each respective point of intersection of the scanning line and signal line; and PA1 terminal electrodes of the scanning lines and signal lines disposed outside the image display area of the active substrate, and PA1 a second translucent insulating substrate with a translucent conductive layer disposed on one of the main surfaces thereof; or PA1 the second translucent insulating substrate with a color filter layer formed thereon, and
The opposing substrate 9 is formed of a glass substrate constituting a translucent insulating substrate having translucent and conductive opposing electrodes.
The active substrate 2 and opposing substrate 9 are separated from each other with a predetermined gap of about several micrometers maintained therebetween by means of such a spacer material as a resin fiber, resin bead and the like, and the space (gap) between the foregoing two substrates is sealed at the peripheral edges of the opposing substrate 9 by the use of a sealant and an encapsulating material, both formed of an organic resin, thereby creating a totally enclosed space, into which liquid crystal is filled.
Color displaying is performed by a color displaying function, which is served by an organic thin film of about 1 to 2 micrometers thick formed as a colored layer containing one selected from a dye and a pigment, or both, disposed on the surface of the opposing substrate 9 on the totally enclosed side. In this case, the glass substrate 9 is also referred to as a color filter.
Depending on the nature of a liquid crystal material, a polarizer is affixed on the upper surface of the opposing substrate 9 or the lower surface of the glass substrate 2, or on both thereof, thereby allowing the liquid crystal panel 1 to act as an electoptic element.
A majority of the liquid crystal panels now in use are a TN (twistnematic) type and each respective panel requires usually two polarizers.
With the liquid crystal panel structured as described in above, a semiconductor integrated circuit chip 3, for example, supplying a driving signal is directly connected to a terminal electrode cluster 6 of the scanning lines according to a COG (Chip-On-Glass) packaging method and a TCP film 4 is connected to a signal electrode cluster 5 of the signal lines and fixed thereon by pressing down a conductive adhesive applied to the connecting points according to a TCP (Tape-Carrier-Package) packaging method outside the image display area of the active substrate 2.
The TCP film 4 is formed of a polyimide resin of around 0.1 mm thick as the base, for example, with terminals made of a copper foil that is gold plated or solder plated. (The terminals are not shown in the drawing.)
For the sake of convenience, the two kinds of packaging method are illustrated on the drawing at the same time but one of the methods is selected as appropriate in practice.
The image display area of the liquid crystal panel 1 is connected with the terminal electrode cluster 5 of the signal lines and the terminal electrode cluster 6 of the scanning lines via wiring channels 7 and 8, respectively. However, the wiring channels 7 and 8 are not necessarily formed of the same conductive material as the terminal electrode clusters 5 and 6.
With the aforementioned liquid crystal panel, a liquid crystal cell comprises a translucent and conductive pixel electrode formed on the active substrate 2, a likewise translucent and conductive opposing electrode formed on the opposing substrate 9 and liquid crystal filled between the two glass substrates.
With an IPS type liquid crystal panel that has been recently put into market with the capability of expanding viewing angles, the translucent electrode (opposing electrode) is no longer required to be disposed on the color filter since the liquid crystal cell comprises a pair of comb like electrodes formed on one (active substrate) of the glass substrates and liquid crystal filled between the two glass substrates. However, a detailed description is not given here to this type liquid crystal panel.
In order to display video images on a liquid crystal panel, electrical signals are fed to terminal electrodes of both scanning lines and signal lines formed according to the aforementioned TCP or COG packaging methods. For a reduction in costs and/or enhancement in reliability involved with packaging by minimizing the number of connecting points, there have been increasing tendencies recently to make heavy use of the COG packaging method.
Although there are a variety of methods and means, by which packaging is performed according to TCP or COG, a typical packaging method that is most frequently employed is described here with reference to FIG. 5.
A plurality of terminal electrodes 5 (6) are disposed on the surface of the active substrate 2 and an insulating layer 15 including a gate insulating layer and a passivation insulating layer is disposed between the adjoining terminal electrodes 5 (6). The insulating layer 15 on each respective terminal electrode is eliminated selectively, thereby making almost all the surface area of each respective terminal electrode 5 (6) free of the insulating layer 15.
Next, after having the active substrate 2 and the color filter (not shown in FIG. 5) put together by adhesion into a panel form in a cell fabrication process, the active substrate 2 and the TCP film 4 with conductive patterns 12 (bump electrodes), each of which is plated with such a conductive material 11 as gold, solder and the like, are connected with each other by an application of pressure and heat via a thermosetting anisotropic conductive film (ACF) 14 containing conductive fine particles 13 in a packaging process.
The conductive patterns 12 (bump electrodes) formed of a copper foil and the base film of the TCP film 4 are joined together fixedly with an adhesive 16.
The conductive fine particle 13 serves as a conductive medium to have the conductive patterns 12 (bump electrodes) and the terminal electrodes 5 (6) connected one another electrically and a typical conductive fine particle 13 is formed of a plastic ball, the surface of which is plated with gold or nickel.
The anisotropic conductive rubber 14 makes a plurality of the conductive fine particles 13 contained therein coagulate and couple with one another to exhibit conductivity when a pressure is applied thereto, as FIG. 3 shows. Therefore, it is preferred to have the surface of any one of the two elements that are joined together made to appear like a convex shape.
With this anisotropic conductive film (ACE) packaging method, the sticking strength of the ACF is reduced when the ACF is heated at a relatively low temperature, thereby allowing the TCP film 4 or semiconductor integrated circuit chip 3 to be peeled off with a physical force. Therefore, the TCP film 4 or semiconductor integrated circuit chip 3 can be peeled off even after having been mounted on the active substrate 2 once and used again, thereby enabling the reworking or recycling of liquid crystal panels to be performed easily.
If no defects are found out with the packaging carried out at a reduced temperature, i.e., tentative packaging (tentative thermosetting), proper packaging (proper thermosetting) at an increased temperature takes place, thereby bringing the packaging process to an end.
As described in above, with the ACF packaging method, the heating process is mandatory. Generally, the reliability in packaging is enhanced as the temperature of the heat applied during the process of packaging is increased. This is assumedly due to an increased strength of the rubber caused by perfect evaporation or sublimation of the solvents contained in the ACF.
Various kinds of ACF materials are available from chemical companies such as Hitachi Chemical, Sony Chemical and the like. A Sony Chemical's product named "Anisorum", for example, is used at a tentative thermosetting temperature of 80.degree. C. to 100.degree. C. and at a proper thermosetting temperature of 180.degree. C. to 200.degree. C.
However, a high processing temperature required in a liquid crystal packaging process has been making it necessary for a polarizer to be attached by adhesion on a liquid crystal panel only after the packaging process. In addition, with a liquid crystal panel of a wide viewing angle, for which there is an increasingly strong demand from the market, it is found out recently that even a small amount of distortion existing in the optical path of a liquid crystal cell results in observing a brightness-dappled display because of an increase in the length of optical path when looked in a slanting direction and resultant difficulty involved with optical design conditions of liquid crystal panels.
Accordingly, the high processing temperature in the packaging process causes distortion to occur on the glass substrate 2 near the terminal electrodes 5 and 6 and creates a danger of the distortion to extend to the vicinity of the image display area, thereby making it necessary for the processing temperature in the packaging process to be lowered. Therefore, a proposal is made on a method for packaging at a low temperature by the use of an ultraviolet curing resin but, as far as the TCP packaging is concerned, there is no established technology to guide ultraviolet rays effectively to an area where packaging and connection take place, thereby creating a problem of making the adoption of an ultraviolet curing resin difficult.
The present invention deals with the foregoing problem and allows a method for mounting a TCP film to display panels at a low temperature to be made available.